The event GW190521 [1]}, [2]} has a special role. It is the most massive event with a confident detection in the GWTC-3 catalog, with masses
\(m_1=91.4^{+29.3}_{-17.5}\, M_{\odot }\)  and \(m_2=66.8^{+20.7}_{-20.7}\, M_{\odot }\)  that, particularly for the primary mass \(m_1\) , fall inside the PISN mass gap with high statistical confidence.
The analysis in ref. [3]} cannot determine if it belongs to a distinct subpopulation or to the high-mass tail of the BBH population considered in the analysis. In the framework of the broken power-law model that we are also using, it can be interpreted as a normal member of the population (while it is clearly an outlier of the `truncated' mass distribution used to fit the GWTC-1 catalog). The underlying hypothesis, for this interpretation, is that the lower edge of the PISN mass gap is not sharp, and events with \(m_1\, \) >\(\)\(\sim \)   45M\( belong to the high-mass tail of the BBH population. However, as remarked also in ref.~\cite {LIGOScientific:2020ibl}, this explanation might pose challenges to our understanding of stellar evolution, since the lower edge of the PISN mass gap is believed to be quite sharp~\cite {Woosley:2016hmi,Farmer:2019jed}.Since the presence of outliers can be particularly relevant for this analysis, as discussed in more detail below, we will perform it both including and excluding GW190521.\)
